The mobile communication system generally refers to any telecommunication system, which enables wireless communication when a user is located within the service area of the system. Examples of such systems are cellular mobile communication systems, such as the GSM (Global System for Mobile communications), or corresponding systems, such as the PCS (Personal Communication System) or the DCS 1800 (Digital Cellular System for 1800 MHz), third-generation mobile systems, such as the UMTS (Universal Mobile Communication System) and systems based on the above-mentioned systems, such as GSM 2+ systems and the future 4th generation systems. One typical example of a mobile communication system is the public land mobile network PLMN.
While the standardization of the UMTS is maturing, the GSM 2+ systems are also evolving towards the UMTS. This means that features of the UMTS, which were not originally planned to be embedded in the GSM 2+, are added to GSM 2+ systems or services, such as GPRS (General Packet Radio Service) or GERAN (GSM/EDGE (Enhanced Data rates for Global Evolution) Radio Access Network). One example of such an added feature is having several signalling radio bearers for one mobile station between the mobile station and the radio access network. In the GERAN, release 5 lu, it has been agreed that the mobile station will have 5 uplink signalling radio bearers, one of which is transmitted over a CCCH (Common Control Channel) or a PCCCH (Packet Common Control Channel). The data of the other four signalling radio bearers may be multiplexed into a layer 2 link established for a user data bearer. The layer 2 link is called a Temporary Block Flow TBF in the GPRS and the GERAN. The layer 2 link, hereinafter called a TBF, is a carrier (i.e. allocated radio resource) that supports the unidirectional transfer of packet data units. The TBF is temporary and it is maintained usually only for the duration of the data transfer.
Besides layer 2, also called a data link layer L2, the protocol architecture of the air interface of a GERAN lu, called a Um-interface, comprises a physical layer L1 and a network layer L3. The lu means that mobile stations are connected to a radio access network GERAN with lu interfaces towards the core network providing the data transfer. The data link layer L2 of the GERAN lu comprises a radio link control RLC sublayer and a medium access control MAC sublayer, which are common for a user plane (i.e. for user data) and for a signalling plane (i.e. for signalling data). The layers above the RLC are a PDCP (Packet Data Convergence Protocol) for the user plane and an RRC (Radio Resource Control) for the signalling plane. Each radio bearer has an RLC instance transmitting the radio bearer data for peer-to-peer information change. The RLC instance transmits information by means of data blocks called packet data units over the air interface on the TBF using e.g. ARQ procedures. Each data block originates from a certain RLC instance. At a transmitting site, the RLC instance forms RLC packet data units by segmenting the upper layer data into data blocks, to which layer 2 control information is added. At a receiving site the RLC instance reassembles the RLC data blocks into upper layer data.
In the GPRS, there is a procedure called a countdown procedure, with which the mobile station informs the network side about how many data blocks are to be sent on the TBF. The mobile station sends a countdown value in each uplink data block to indicate the current number of remaining data blocks for the uplink TBF. The network schedules resources for this TBF on the basis of the QoS (quality of service) parameters of the user data bearer and the amount of data to be sent on the user data bearer, for example. The QoS parameters indicate the properties that the user data bearer needs, such as delay requirements.
One of the problems associated with the above arrangement is that when one or more radio bearer(s) (and hence RLC instances) can be stealing capacity from a user radio bearer A, i.e. are multiplexed to a TBF established for the user radio bearer A, there is no mechanism to take into account the amount of data of other bearers transmitting data blocks on the TBF of the user radio bearer A. Therefore the network does not know how much resources and how frequently it should allocate for the TBF.